Wheel rotation detecting device

ABSTRACT

A wheel rotation detecting device including a sensor unit that is supported on a stationary ring which does not rotate even when the wheel is in use, and the rotation of the wheel that is attached to a rotary ring can be detected by a rotation detecting sensor held within the sensor unit. Within the sensor unit, in addition to a rotation detecting sensor, there are disposed other sensors such as a temperature sensor and a vibration sensor, thereby allowing detection of the rotation speed and the rotation number of the wheel supported on the rotary ring, as well as detection of other car driving conditions.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wheel rotation detecting device whichdetects the rotation speed (or rotation number) of a wheel of a carsupported on a suspension and also detects the conditions of a rollingbearing unit portion supporting the wheel of the car, such as thetemperature or vibration thereof.

2. Description of the Related Art

To obtain the rotation speed of a wheel in order to be able to controlan antilock brake system (ABS) or a traction control system (TCS), inthe related art, there are known various kinds of wheel supportingrolling bearing units with a rotation speed detecting device eachstructured such that a rotation speed detecting device is incorporatedinto a rolling bearing unit used to support the wheel on a suspension ofa car. Here, as an example of a wheel supporting rolling bearing unitwith a rotation speed detecting device which is used for the abovepurpose, FIG. 19 shows a wheel supporting rolling bearing unit which isdisclosed in Japanese Patent No. 2838701.

An outer ring 1, which corresponds to a stationary ring, is supported ona knuckle forming a suspension by an outward-facing-flange-shapedmounting portion 2 formed on the outer peripheral surface of the outerring 1 and, even when the rolling bearing unit is in use, the outer ring1 is not rotatable. A rotary ring 3 is disposed on the inside diameterside of the outer ring 1; and, the rotary ring 3 is structured such thatan inner ring 5 is fitted into and fixed to the inner end portion of ahub 4 (here, the term “inner side with respect to the axial direction”means the width-direction central side of the rolling bearing unit withrespect to a car; and, in FIGS. 1, 14 and 19, on the right side).Between outer ring raceways 6, 6, which are formed in the innerperipheral surface of the outer ring 1 and respectively serve asstationary side raceways, and inner ring raceways 7, 7 which are formedin the outer peripheral surface of the hub 4 and inner ring 5 andrespectively serve as rotary side raceways, there are interposed tworows of rolling elements, that is, balls 8, 8 each row including aplurality of rolling elements in such a manner that they are rollablewhile they are held by their respective retainers 9, 9.

The above-structured rotary ring 3 is rotatably supported on the insidediameter side of the outer ring 1. On the outer end portion (here, theterm “outer side with respect to the axial direction” means thewidth-direction end portion side of the rolling bearing unit withrespect to a car; and, in FIGS. 1, 14 and 19, on the left side) of thehub 4 forming the rotary ring 3, there is disposed a flange 10 which isused to support a wheel (not shown). Also, seal rings 11, 11 areinterposed between the inner peripheral surfaces of the two end portionsof the outer ring 1 and the middle portion outer peripheral surface ofthe hub 4 and the outer peripheral surface of the inner end portion ofthe inner ring 5, and, these seal rings 11, 11 shut off a space 12, inwhich the balls 8, 8 are disposed, from the outside, thereby being ableto prevent grease enclosed in the space 12 from leaking out therefrom tothe outside, and also to prevent a foreign substance floating in theoutside from moving into the space 12.

Also, an encoder 13 is fitted with and fixed to the outside of themiddle portion of the hub 4, namely, the portion extending between thetwo rows of balls 8, 8 in an interference fit manner. The encoder 13 isformed of magnetic metal material such as soft steel into acircular-ring shape; and, on the outer peripheral surface of the encoder13, there are formed gear-shaped uneven portions (composed of recessedportions and projected portions) to thereby cause the magneticcharacteristics of the present outer peripheral surface to varyalternately and at regular intervals with respect to the circumferentialdirection. On the other hand, in the middle portion of the outer ring 1,a rotation detecting sensor 14 is inserted into and supported by amounting hole 15 which is formed in such a manner that it can bring theinner and outer peripheral surfaces of the outer ring 1 intocommunication with each other; and, a detecting portion, which is formedin the leading end face (in FIG. 19, the lower end face) of the rotationdetecting sensor 14, is disposed near to and opposed to the outerperipheral surface of the encoder 13.

When the above-structured wheel supporting rolling bearing unit with arotation speed detector of the related art is in use while it isassembled between the suspension and wheel, in case where this wheel isrotated, the recessed portions and projected portions existing on theouter peripheral surface of the encoder 13 pass alternately through thedetecting surface of the rotation detecting sensor 14. As a result ofthis, the density of magnetic flux flowing in the rotation detectingsensor 14 varies, whereby the output of the rotation detecting sensor 14varies. A frequency, at which the output varies, is in proportion to therotation speed of the wheel and, therefore, in case where the outputsignal of the rotation detecting sensor 14 is sent to a control unit(not shown), the ABS or TCS can be controlled properly. Also, therotation number of the wheel can be obtained from the number of times ofthe variations of the output of the rotation detecting sensor 14. Thanksto this, recently, the output signal of the rotation detecting sensor 14has been used as a signal to control not only the ABS and TCS but also acar navigation system and an ITS (Intelligent Transport System).

In the case of the above-mentioned wheel supporting rolling bearing unitwith a rotation speed detector of the related art, the rotation speedand rotation number of the wheel can be detected but the otherconditions of the wheel supporting rolling bearing unit cannot bedetected. On the other hand, due to the rapid progress of a cartechnology in recent years, there arises the need to obtain more piecesof information from the wheel supporting rolling bearing unit.

For example, in case where it is possible to know the temperature of awheel supporting rolling bearing unit portion of a car, an increase inthe temperature of the wheel supporting rolling bearing unit portion andthe overheated condition of a brake portion of a car can be detected.The increase in the temperature of the wheel supporting rolling bearingunit portion not only provides important data in knowing the life of thepresent wheel supporting rolling bearing unit itself but also can showthe overheated condition of the brake portion to thereby give a warningto a driver before a dangerous condition such as vapor lock occurs. Bythe way, in case where a speed signal from a rotation detecting sensoris combined with a temperature signal from a temperature sensor,generation of heat due to the friction loss of the present rollingbearing unit can be corrected. Therefore, even in a moving body such asa vehicle in which the temperature always varies according to variationsin the rotation speed, the accuracy of detection of the temperature inthe abnormality of the present rolling bearing unit can be enhanced.Also, by measuring the magnitude of the vibrations and the wavelengthsof the wheel supporting rolling bearing unit portion and by analyzingthe frequencies thereof, there can be obtained important data in knowingthe life of the wheel supporting rolling bearing unit in addition to theconditions of the road surfaces and the conditions of the air pressuresof tires. In case where proper knowledge of the road conditions isobtained, the automatic change of the damping force of a damper attachedto the suspension can be executed properly; and, in case where the tireair pressure can be estimated, it is possible not only to give a warningwhen the tire air pressure is abnormal but also to increase or decreasethe tire air pressure. This can prevent an accident such as tire burstwhich may occur when a vehicle runs at a high speed with a low tire airpressure. Further, a proper knowledge of the life of the wheelsupporting rolling bearing unit can tell the driver the remaining lifethereof before the car becomes impossible to run any further and thuscan give a warning to the driver in such a condition that the driver candrive the car up to a garage.

To know the above-mentioned temperatures and vibrations, a temperaturesensor and a vibration sensor (an acceleration sensor) may be assembledto a portion of the wheel supporting rolling bearing unit. However, incase where these sensors are assembled independently of the rotationdetecting sensor, the weight and assembling space of the wheelsupporting rolling bearing unit increase, and the number of assemblingman-hour increases to thereby increase the manufacturing cost of the carunfavorably.

SUMMARY OF THE INVENTION

The present invention aims at eliminating the above-mentioned drawbacksfound in the wheel rotation detecting device of the related art.Accordingly, it is an object of the invention to provide a wheelrotation detecting device which is capable of detecting the rotationspeed or rotation number of a wheel supported on a rotary ring and theother conditions such as temperatures and vibrations helpful in drivinga car.

In attaining the above object, according to the invention, there isprovided a wheel rotation detecting device which, similarly to aconventionally known wheel rotation detecting device such as theabove-mentioned wheel supporting rolling bearing unit with a rotationspeed detector, comprises a stationary ring, a rotary ring, a pluralityof rolling elements, and encoder, and a rotation detecting sensor (afirst sensor).

In the present wheel rotation detecting device, the stationary ring issupported on a suspension of a car and does not rotate even when it isin actual use.

And, the rotary ring, in a state where it supports a wheel thereon, canrotate together with the wheel.

Also, the rolling elements are rollably interposed between a stationaryside raceway formed in the peripheral surface of the stationary ring anda rotary side raceway formed in the peripheral surface of the rotaryring.

The encoder is used to detect the rotation of the rotary ring and issupported on the rotary ring or on a part mounted on the rotary ring.

The rotation detecting sensor, with a detecting portion thereof opposedto the encoder, is supported on the stationary ring itself, or a partfixed to the stationary ring such as a cover or a portion of thesuspension.

Especially, in the present wheel rotation detecting device according tothe invention, within a holder holding the rotation detecting sensor asa first sensor therein, besides the rotation detecting sensor, there isdisposed at least a second sensor which is used to detect the conditionof a wheel supporting rolling bearing unit portion of a car.

As the second sensor, for example, there can be used a temperaturesensor for monitoring the temperature of the wheel supporting rollingbearing unit portion, or a vibration sensor (an acceleration sensor) formeasuring the vibrations of the present wheel supporting rolling bearingunit portion.

According to the above-structured wheel rotation detecting device of theinvention, similarly to the previously-described wheel rotationdetecting device of the related art, the wheel can be rotatablysupported on the suspension and, at the same time, using the rotationdetecting sensor, one or both of the rotation speed and rotation numberof the wheel in the car running condition can be detected. Further,using the second sensor, the other conditions of the wheel supportingrolling bearing unit portion such as the temperature and vibrationthereof than the rotation speed of the wheel can be detected.

Moreover, since the second sensor is disposed within a holder holdingthe rotation detecting sensor therein, there is no possibility that thesecond sensor may increase the weight and assembling space of the wheelsupporting rolling bearing unit portion and may increase the number ofassembling man-hour to thereby increase the manufacturing cost of a carunfavorably. Also, in case where the second sensor is a temperaturesensor, this temperature sensor is disposed within the same holderholding therein other sensors including the rotation detecting sensor,the detect signal of the temperature sensor can be used to correct theoutputs of the other sensors according to the temperatures, which makesit possible to further enhance the accuracy of the detected data.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a section view of a first embodiment according to theinvention;

FIG. 2 is a section view of a sensor unit to be incorporated into thefirst embodiment;

FIG. 3 is a section view of a sensor unit to be incorporated into asecond embodiment according to the invention;

FIGS. 4A to 4C are explanatory perspective views of an installationstate when there is used a vibration sensor capable of detecting onlythe vibration in one direction;

FIGS. 5A to 5C are explanatory perspective views of an installationstate when there is used a vibration sensor capable of detectingvibrations in two directions;

FIGS. 6A to 6C are explanatory perspective views of an installationstate when there is used a vibration sensor capable of detectingvibrations in three directions;

FIG. 7 is a section view of a sensor unit to be incorporated into athird embodiment according to the invention;

FIG. 8 is a section view of a sensor unit to be incorporated into afourth embodiment according to the invention;

FIG. 9 is a section view of a fifth embodiment according to theinvention;

FIG. 10 is a section view of a sensor unit to be incorporated into thefifth embodiment;

FIG. 11 is a section view of a sensor unit to be incorporated into asixth embodiment according to the invention;

FIG. 12 is a section view of a sensor unit to be incorporated into aseventh embodiment according to the invention;

FIG. 13 is a section view of a sensor unit to be incorporated into aneighth embodiment according to the invention;

FIG. 14 is a block diagram of a first example of a circuit used todetect the abnormality of a rolling bearing unit;

FIG. 15 is a block diagram of a second example of the above circuit;

FIG. 16 is a block diagram of a third example of the above circuit;

FIG. 17 is a block diagram of a fourth example of the above circuit;

FIG. 18 is a block diagram of a fifth example of the above circuit; and,

FIG. 19 is a section view of an example of a structure of the relatedart.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, FIGS. 1 and 2 shows a first embodiment according to the invention.In the first embodiment, a hub 4 formed in a hollow cylindrical shapehas a flange 10 on the outer peripheral surface of the outer end portionthereof. A wheel and a disk rotor forming a brake device are fixed to aflange 10 by a plurality of studs (not shown). On the outer peripheralsurface of the middle portion of the hub 4, there is formed an outsideinner ring raceway 7, while an inner ring 5 including an inside innerring raceway 7 on the outer peripheral surface thereof is fitted intoand fixed to the outer portion of a stepped portion 16 provided on theinner end portion of the hub 4, thereby forming a rotary ring 3. Aspline hole 17 is formed in the central portion of the hub 4 forming thethus-structured rotary ring 3; and, in an assembling state of a car, aspline shaft attached to a constant velocity universal joint (not shown)is inserted into the spline hole 17.

On the other hand, on the periphery of the rotary ring 3, there isdisposed an outer ring 1 concentrically with the rotary ring 3, whilethe outer ring 1 includes a double row of outer ring raceways 6, 6formed on the inner peripheral surface thereof and a mounting portion 2formed on the outer peripheral surface thereof. The mounting portion 2is used to support and fix the outer ring 1 onto a suspension (notshown) such as knuckle. Also, two groups of a plurality of balls 8, 8,each forming a rolling element, are interposed between the outer ringraceways 6, 6 and the inner ring raceways 7, 7, whereby the rotary ring3 for fixing the wheel thereto can be rotatably supported on the insidediameter side of the outer ring 1 to be fixed to the suspension. By theway, in the case of a car rolling bearing unit which is heavy in weight,as the rolling elements, instead of the illustrated balls 8, 8, therecan also be used tapered rollers. Also, instead of the outside innerring raceway 7 being directly formed on the outer peripheral surface ofthe hub 4, it can also be formed on the outer peripheral surface of aninner ring which is disposed separately.

Also, seal rings 11, 11 are interposed between the inner peripheralsurfaces of the two end portions of the outer ring 1 and the outerperipheral surface of the middle portion of the hub 4, the outerperipheral surface of the inner end portion of the inner ring 5. Theseal rings 11, 11 are respectively used to close the openings of the twoend portions of a space 12 in which the plurality of balls 8, 8 aredisposed. And, the seal rings 11, 11 prevent grease enclosed into thespace 12 from leaking therefrom to the outside and also prevent foreignsubstances floating in the outside from moving into the space 12.

Also, a cylindrical surface portion 18 is formed in the portion of theouter peripheral surface of the middle portion of the hub 4 that extendsbetween the outside inner ring raceway 7 and the stepped portion 16, andthe cylindrical surface portion 18 is concentric with the hub 4. And, anencoder 13 is fitted with and fixed to the outer portion of thecylindrical surface portion 18 in an interference fit manner. Theencoder 13 is made of a magnetic metal plate such as an SPCC steel plateand is formed in a cylindrical shape as a whole and, in theaxial-direction middle portion of the encoder 13, there are formed alarge number of through holes 19, 19 at regular intervals along thecircumferential direction thereof, while these through holes 19, 19function as component reducing portions of the encoder 13. These throughholes 19, 19 are respectively formed in a slit which is long in theaxial direction thereof (in FIG. 1, in the right and left direction).Also, the portions extending between the through holes 19, 19 mutuallyadjoining in the circumferential direction of the encoder 13 are formedin pillar portions which function as solid portions. This structureallows the magnetic characteristic of the axial-direction middle portionouter peripheral surface of the encoder 13 to vary alternately and atregular intervals along the circumferential direction thereof.

On the other hand, a mounting hole 15 a is formed in the portion of theaxial-direction middle portion of the outer ring 1 that is opposed tothe outer peripheral surface of the encoder 13, while the mounting hole15 a penetrates through the outer peripheral surface of the outer ring 1up to the inner peripheral surface thereof. And, a sensor unit 20 isinserted into the mounting hole 15 a from an opening which is formed onthe outside diameter side of the outer ring 1, while the leading endface (in FIG. 1, lower end face) of the sensor unit 20 is disposed nearto and opposed to the peripheral surface of the encoder 13. In orderthat the sensor unit 20 can be freely inserted into the mounting hole 15a in this manner, the mounting portion 2 is formed such that it isdiscontinuous in the portion thereof existing in the periphery of theoutside diameter side opening of the mounting hole 15 a and, instead, amounting seat 21 is formed on the outer peripheral surface of the outerring 1. By screwing a flange 22 formed in the base end portion (in FIG.1, the upper end portion) of the sensor unit 20 to the mounting seat 21,the sensor unit 20 can be fixed to the outer ring 1. Also, an O-ring 23is interposed between the inner peripheral surface of the mounting hole15 a and the outer peripheral surface of the sensor unit 20, to therebyseal between these surfaces.

In the case of the sensor unit 20, as shown in FIG. 2, within a holder(case) 24 formed of synthetic resin, there are disposed (embedded andsupported) a rotation detecting sensor 25 and a temperature sensor 26.The rotation detecting sensor 25 comprises a magnet detect element 27, apermanent magnet 28 and a waveform shaping circuit 29. The magnet detectelement 27 is formed by a hall element, an MR element or the like andvaries its characteristic according to the quantities of magnetic fluxpassing therethrough. The permanent magnet 28 is a source of generationof magnetic flux passing through the magnet detect element 27 and ismagnetized in the vertical direction in FIG. 2. Further, the waveformshaping circuit 29 shapes the waveform of a signal (arranging the signalinto a square wave) issued according to variations in the characteristicof the magnet detect element 27. And, the magnet detect element 27 isdisposed near to and opposed to the axial-direction middle portion outerperipheral surface of the encoder 13 with a minute clearance 30 betweenthem. On the other hand, the temperature sensor 26, which is composed ofa thermistor, is embedded into and supported by the leading end portionof the holder 24 and is free to detect the temperature of the interiorof the space 12 within which the balls 8, 8 are disposed. The detectsignals of the rotation detecting sensor 25 and temperature sensor 26,which form the sensor unit 20, are taken out through a harness 31 guidedfrom the base end face of the holder 24 and are then transmitted to acontrol unit (not shown).

The rotation detecting sensor 25 forming the above-mentioned sensor unit20 detects one or both of the rotation speed and rotation number of thewheel in the following manner. That is, when the encoder 13 fitted withand fixed to the outer portion of the hub 4 is rotated as the wheel isrotation, the through holes 19, 19 formed in the axial-direction middleportion of the encoder 13 and the pillar portions existing between thethrough holes 19, 19 mutually adjoining in the circumferential directionof the encoder 13 pass alternately through the vicinity of the magnetdetect element 27. As a result of this, the quantities of magnetic fluxflowing in the magnet detect element 27 vary, which causes the output ofthe rotation detecting sensor 25 to vary. Since a frequency at whichthis output varies is in proportion to the rotation speed of the wheel,in case where the output signal is input to the control unit (not shown)through the harness 31, the rotation speed of the wheel can be found aswell as the ABS and TCS can be controlled properly. Also, because therotation number of the wheel can be obtained from the number of times ofvariations of the present output and also the running distance of thecar can be found from the thus-obtained rotation number, the rotationdetecting sensor 25 can be used to control a car navigation system.

On the other hand, the temperature sensor 26 detects the temperature ofthe interior of the space which is present within the wheel supportingrolling bearing unit and similarly sends a detect signal through theharness 31 to the control unit (not shown). And, this makes it possibleto confirm an increase in the temperature of the wheel supportingrolling bearing unit portion and the overheated condition of the brake.The increase in the temperature of the wheel supporting rolling bearingunit portion not only provides important data in knowing the life of thewheel supporting rolling bearing unit itself but also can tell theoverheated condition of the brake and thus can give an alarm to thedriver before a dangerous condition such as vapor lock occurs.

By the way, because the overheated condition of the brake is transmittedfrom the disk rotor to the hub 4, preferably, the temperature sensor 26may be disposed on the leading end face of the sensor unit 20 in such amanner that it is situated near to and opposed to the hub 4. On theother hand, the increase in the temperature of the wheel supportingrolling bearing unit portion can also be found from the temperature ofthe outer ring 1. And, in order to measure the temperature of the outerring 1, the temperature sensor 26 may also be disposed on the portion ofthe middle portion of the holder 24 that is opposed to the innerperipheral surface of the mounting hole 15 a. In any case, by disposingthe temperature sensor 26 in such a manner that it is situated near toor in contact with the portion to be measured, the temperature of theportion to be measured can be measured accurately, the abnormality ofthe wheel supporting rolling bearing unit and the overheated conditionof the brake can be detected at an early stage thereof, and thus analarm can be issued properly.

Also, since the temperature sensor 26, which functions as the secondsensor, is embedded into and supported on the interior of the sameholder 24 for holding the rotation detecting sensor 25, the provision ofthe temperature sensor 26 neither increases the weight and assemblingspace of the sensor unit 20 excessively nor increases the number ofassembling man-hour; and, therefore, the provision of the temperaturesensor 26 does not increase the manufacturing cost of the carunfavorably. And, conductors, which are used to transmit the detectsignals of the respective sensors 25, 26 to the control unit, can becollected together into the single harness 31 which is stored within thesame sheath. This makes it possible to reduce the weight of the harness31 and simplify the wiring operation.

Next, FIG. 3 shows a second embodiment according to the invention.Specifically, a sensor unit 20 a employed in the present embodimentcomprises, within a holder 24 a formed of synthetic resin, not only amagnet detect element 27, a permanent magnet 28, and a waveform shapingcircuit 29 respectively used to form a rotation detecting sensor 25 butalso a vibration sensor 32 which is used as a second sensor, while thesecomponents are respectively embedded in and supported by the holder 24a. The vibration sensor 32 is structured such that, for example, asmall-sized acceleration sensor using a piezoelectric element and asignal processing circuit are mounted on a substrate 33 and, in thisstate, they are molded into the holder 24 a. Referring to the positionof the vibration sensor 32, in order to be able to make the sensor unit20 a compact as a whole, preferably, as shown in FIG. 3, with respect tothe axial direction (in FIG. 3, the vertical direction) of the holder 24a, the vibration sensor 32 may be disposed in series with the magneticdetect element 27 and permanent magnet 28 and nearer to the base endside (in FIG. 3, the upper end side) of the holder 24 a than these twocomponents.

The structure of the second embodiment in which the above sensor unit 20a is fixed to the outer ring 1 (see FIG. 1) forming a wheel supportingrolling bearing unit and the output signals of the sensors 25, 32 aretaken out, and also the operation of the second embodiment to detect therotation speed of the wheel using the rotation detecting sensor 25 aresimilar to those in the previously described first embodiment.

Especially, in the case of the present embodiment, since the vibrationsensor 32 is embedded into and supported by the synthetic-resin-madeholder 24 a and is thereby united with the sensor unit 20 a as anintegral body and the thus-integrally-united sensor unit 20 a is fixedto the outer ring 1 with no play between them, the vibrations of theouter ring 1 can be measured with accuracy. Because the vibrationstransmitted from the wheel to the hub 4 are transmitted to the outerring 1 through the balls 8, 8 (see FIG. 1), in case where a signaloutput from the vibration sensor 32 is input into a control unit (notshown), the uneven portions of the road surface with which the wheel isin contact, the air pressure of the tire, and the acceleration ordeceleration conditions of the car can be detected. And, the dampingamount of a damper incorporated into the suspension can be automaticallyadjusted and the output of the engine can be controlled. Also, anabnormal vibration, which occurs because the wheel supporting rollingbearing unit reaches its lifetime, can be detected and thus an alarm canalso be given to the driver properly.

By the way, the vibrating direction to be detected by the vibrationsensor 32 can be freely adjusted by regulating the direction of thevibration sensor 32 in a state (in amounted state) where the wheelsupporting rolling bearing unit is supported on the suspension. Forexample, assuming that the vibration sensor 32 is composed of anordinary piezoelectric element, the vibrating direction detectable bythe vibration sensor 32 is any one of an a-axis direction, a b-axisdirection and a c-axis direction respectively shown in FIG. 4A.Vibrations applied in directions at right angles to these respectiveaxes can be little detected, whereas, in the case of vibrations appliedin directions inclined with respect to these axes, the vibrationcomponents parallel to these axes can be detected.

Therefore, here, states shown in FIGS. 4B and 4C are taken as examplesof the mounted or installation states of the vibration sensor 32; and,with respect to these mounted states of FIGS. 4B and 4C, the X directionis assumed to be the transverse direction of a vehicle, the Y directionis assumed to be the longitudinal direction of the vehicle and the Zdirection is assumed to be the vertical direction of the vehicle. Thatis, under such assumption, the vibration detection is checked. By theway, in the states of FIGS. 4B and 4C {and, in states shown in FIGS. 5Ato 5C and 6A to 6C which will be discussed later}, arrow marks shownwithin the vibration sensor 32 respectively express the vibrationdirections to be detected by the vibration sensor 32. Firstly, as shownin FIG. 4B, in case where the detecting direction of the vibrationsensor 32 is coincident with the Z direction, the vibrations in thevertical direction of the vehicle can be detected effectively, whereasthe vibrations in the advancing direction and in the transversedirection cannot be detected. Also, in the case of the vibrationsapplied in the inclined direction with respect to the verticaldirection, the components thereof in the vertical direction can bedetected. Next, as shown in FIG. 4C, in case where the detectingdirection of the vibration sensor 32 is coincident with the Y direction,the vibrations in the longitudinal direction of the car can be detectedeffectively, whereas the vibrations in the vertical direction and in thetransverse direction cannot be detected. Also, in the case of thevibrations applied in the inclined direction with respect to thelongitudinal direction, the components thereof in the longitudinaldirection can be detected. By the way, in FIGS. 4B and 4C (and FIGS.5A-6C which will be discussed later), reference character 35 designatesa signal processing circuit which is used to process the detect signalsof the vibration sensor 32.

Also, as shown in FIG. 5, by properly selecting the number of vibrationsensors mounted, the mounting directions thereof, and the kinds thereof,the vibrations in two of the X, Y and Z directions can be detected.Firstly, as shown in FIG. 5A, in case where not only two vibrationsensors 32 a, 32 b are fixed to a single substrate 33 but also thedetecting direction of one vibration sensor 32 a {in FIG. 5A, the lowervibration sensor} is made to coincide with the Z direction and the othervibration sensor 32 b {in FIG. 5A, the upper vibration sensor} is madeto coincide with the Y direction, the vibrations in the vertical andlongitudinal directions can be detected effectively, whereas thevibrations in the transverse direction cannot be detected. In the caseof the vibrations applied in the inclined directions with respect to thevertical and transverse directions, the components thereof in thevertical and longitudinal directions can be detected. Next, as shown inFIG. 5B, in case where there is used a vibration sensor 32 c thedetecting direction of which is a direction intermediate between the Yand Z directions (that is, a direction having an angle of 45° withrespect to the Y and Z directions), the vibrations in the longitudinaldirection and the vibrations in the vertical direction can be detectedas the resultant forces thereof. In this case, the vibrations in thetransverse direction cannot be detected but, by changing the detectingdirection, the vibrations in the transverse direction can also bedetected, or, the vibrations in the transverse direction and thevibrations in the longitudinal or vertical direction can be detected asthe resultant forces thereof. Further, as shown in FIG. 5C, in casewhere there is used a vibration sensor 32 d capable of detectingvibrations in two directions intersecting at right angles with eachother and the detecting direction of the vibration sensor 32 d is madeto coincide with the Y and Z directions, the vibrations in thelongitudinal and vertical directions can be detected, whereas thevibrations in the transverse direction cannot be detected. By the way,the combination of the detecting directions is not limited to theabove-mentioned combination of the Y and Z directions but any ofcombinations of the X and Z directions and the X and Y directions canalso be used.

Further, as shown in FIGS. 6A to 6C, by properly selecting the number ofvibration sensors to be mounted, the mounting directions thereof, andthe kinds thereof, the vibrations in all of the X, Y and Z directionscan be detected. Firstly, as shown in FIG. 6A, in case where not onlythree vibration sensors 32 a, 32 b, 32 e are fixed to a single substrate33 but also the detecting directions of these three vibration sensors 32a, 32 b, 32 e are made to respectively coincide with the X, Y, and Zdirections, the vibrations in the transverse, longitudinal and verticaldirections can all be detected effectively. Next, as shown in FIG. 6B,even in case where there are mounted a vibration sensor 32 e having adetecting direction coincident with the X direction and a vibrationsensor 32 d having a detecting direction coincident with the Y and Zdirections, the vibrations in the transverse, longitudinal and verticaldirections can all be detected effectively. Further, as shown in FIG.6C, even in case where there is used a vibration sensor 32 f capable ofdetecting the vibrations in three directions intersecting at rightangles with one another and the detecting direction of the vibrationsensor 32 f is made to coincide with the X, Y and Z directions, thevibrations in the transverse, longitudinal and vertical directions canall be detected effectively. In a word, according to vibrationinformation required, proper vibration sensors may be used in a propernumber,

Next, FIG. 7 shows a third embodiment according to the invention.Specifically, a sensor unit 20 b employed in the present embodimentcomprises, within a holder 24 b formed of synthetic resin, a rotationdetecting sensor 25 and a temperature sensor 26 and a vibration sensor32 respectively used as second sensors, while these components arerespectively embedded in and supported by the interior of the holder 24b. The operation of the temperature sensor 26 is similar to that of thefirst embodiment and the operation of the vibration sensor 32 is similarto that of the second embodiment. Therefore, the equivalent partsthereof are given the same designations and thus the duplicatedescription thereof is omitted here. By the way, as the vibration sensor32, any one of the vibration sensors shown in FIGS. 4A-6C can be used.

Next, FIG. 8 shows a fourth embodiment according to the invention.Specifically, in the case of a sensor unit 20 c used in the presentembodiment, a synthetic-resin-made holder 24 c including a rotationdetecting sensor 25, a temperature sensor 26 and a vibration sensor 32embedded therein is held within a case 34 which is made of non-magneticmetal such as aluminum, copper and non-magnetic stainless steel.Provision of such case 34 not only can enhance the strength of thesensor unit 20 c but also makes it hard for the rotation detectingsensor 25 to be influenced by external magnetic flux. By the way, thestructure using such case 34 can also be combined with the structureused in the first embodiment shown in FIG. 2, or the structure used inthe third embodiment shown in FIG. 7. In the present embodiment as well,as the vibration sensor 32, any one of the vibration sensors shown inFIGS. 4A-6C can be used.

Also, the encoder 13 (see FIG. 1) may be a gear-like device havinguneven portions (projected and recessed portions) alternately formed inthe peripheral direction thereof, or maybe a multi-pole magnet having Sand N poles formed alternately at regular intervals with respect to thecircumferential direction thereof. In case where an encoder made of amulti-pole magnet is used, the permanent magnet on the rotationdetecting sensor side can be omitted. Description will be given below ofa specific structure, in which such encoder made of a multi-pole magnetis used, with reference to the fifth to eighth embodiments of theinvention respectively shown in FIGS. 9 to 13. Further, the kinds andstructures of the vibration sensor 32, substrate 33 and signalprocessing circuit 35 cooperating together in forming the vibrationdetector are not limited to those described above. For example, thevibration sensor 32 may be of other types than the piezoelectric type,such as an electrostatic capacity type, a strain gauge type, and amicro-machine type, or may incorporate the signal processing circuit 35therein, or may be composed of an IC device. Also, as the temperaturesensor, besides the above-mentioned thermistor, there can also be used athermoelectric couple, a platinum temperature measuring member, or atemperature measuring IC. Further, in the illustrated embodiment,between the balls 8, 8 which function as rolling elements, there areinterposed the sensor unit 20 and encoder 13. However, the invention isnot limited to this structure but, for example, these parts 20, 13 maybe disposed outside or inside the balls 8, 8; or, the encoder 13 may bedisposed on the end face of the rotary ring or a seal and the sensorunit 20 may be disposed such that it is opposed to the encoder 13. Inshort, the encoder 13 may be disposed on the rotary ring or on a partrotatable with the rotary ring, and the sensor unit 20 may be disposedon the stationary ring or a part mounted on the stationary ring. In thisrespect, various modifications are possible without departing from thescope of the invention.

Next, FIGS. 9 and 10 show a fifth embodiment according to the invention.In the present embodiment, as an encoder 13 a which is fitted with andfixed to the outer portion of the hub 4 in order to detect the rotationspeed of the hub 4, there is used an encoder made of a permanent magnet.This encoder 13 a can be formed such that an encoder main body made of arubber magnet including ferrite powder or rare earth system magnetpowder mixed therein is attached to the whole of the outer peripheralsurface of a cylindrical-shaped core. The encoder main body may also bemade of a plastic magnet or a bonded magnet. Also, the core may beformed of metal or synthetic resin. More preferably, the core may bemade of a magnetic metal plate such as a steel plate, because theintensity of magnetic flux generated from the outer peripheral surfaceof the encoder main body can be increased: that is, even in case wherethe minute clearance 30 between the outer peripheral surface of theencoder main body and the detecting portion of the rotation detectingsensor disposed within the holder 24 is widened, the reliability of therotation detection can be secured. Further, the encoder 13 a may also bestructured in the following manner: that is, the core metal is omittedand the encoder main body is directly fixed by resin molding or byadhesion to the outside diameter surface of the hub 4.

In any case, the encoder main body is magnetized in the diameterdirection thereof and the magnetizing directions of the encoder mainbody vary alternately at regular intervals with respect to thecircumferential direction thereof. Therefore, on the outer peripheralsurface of the encoder 13 a, there are disposed S and N polesalternately at regular intervals with respect to the circumferentialdirection thereof. By the way, generally, the magnetizing pattern of theencoder main body is set so as to vary alternately at regular intervals.However, this is not always limitative. For example, as disclosed inJP-A-2000-346673, in case where there is employed a magnetizing patternin which S poles, N poles and non-magnetized areas are arranged so as torepeat one another, not only the rotation speed but also the rotationdirection can be detected. In brief, a desired magnetizing pattern maybe employed according to the function that is required.

In any case, in view of the fact that a permanent magnet is used as theencoder 13 a, on the sensor unit 20′ mounted into the mounting hole 15 aof the outer ring 1, there is not disposed such a permanent magnet 28 asshown in FIG. 2. That is, in the case of the sensor unit 20′, a magnetdetect element 27 and a waveform shaping circuit 29 functioning as therotation detecting sensor 25 a, and a temperature sensor 26 are disposedwithin (embedded into and supported by) the sensor unit 20′. Thestructures and operations of the remaining portions of the fifthembodiment are similar to those of the first embodiment shown in FIGS. 1and 2. Therefore, the equivalent parts thereof are given the samedesignations and thus the duplicate description thereof is omitted here.

Next, FIG. 11 shows a sixth embodiment according to the invention. Inthe case of a sensor unit 20 a′ used in the present embodiment, within aholder 24 a formed of synthetic resin, there are disposed (embedded andsupported) not only a magnet detect element 27 and a waveform shapingcircuit 29 cooperating together in forming a rotation detecting sensor25 a, but also a vibration sensor 32 which serves as a second sensor.Except that no permanent magnet is incorporated into the rotationdetecting sensor 25 a because the encoder 13 a (see FIG. 9) is formed ofa permanent magnet, the present embodiment is similar to the previouslydescribed second embodiment shown in FIG. 3. Therefore, the equivalentparts thereof are given the same designations and thus the duplicatedescription thereof is omitted here.

Next, FIG. 12 shows a seventh embodiment according to the invention. Inthe case of a sensor unit 20 b′ used in the present embodiment, within aholder 24 b formed of synthetic resin, there are disposed (embedded andsupported) not only a rotation detecting sensor 25 a but also atemperature sensor 26 and a vibration sensor 32 which respectivelyfunction as second sensors. Except that no permanent magnet isincorporated into the rotation detecting sensor 25 a because a permanentmagnet is used as the encoder 13 a (see FIG. 9), the present embodimentis similar to the previously described third embodiment shown in FIG. 7.Therefore, the equivalent parts thereof are given the same designationsand thus the duplicate description thereof is omitted here.

Next, FIG. 13 shows an eighth embodiment according to the invention. Inthe case of a sensor unit 20 c′ used in the present embodiment, asynthetic-resin-made holder 24 c embeddedly supporting a rotationdetecting sensor 25 a and a vibration sensor 32 is held within a case 34made of non-magnetic metal such as aluminum, copper, or non-magneticstainless steel. Except that no permanent magnet is incorporated intothe rotation detecting sensor 25 a because a permanent magnet is used asthe encoder 13 a (see FIG. 9), the present embodiment is similar to thepreviously described fourth embodiment shown in FIG. 8. Therefore, theequivalent parts thereof are given the same designations and thus theduplicate description thereof is omitted here.

In the structures respectively employed in the above-mentionedembodiments shown in FIGS. 2, 3, 7, 8, 10-13, the spaces forinstallation of the respective sensor units 20, 20 a, 29 b, 20 c, 20′,20 a′, 29 b′, 20 c′ are extremely limited. Especially, as shown in FIGS.1 and 9, in the structures in which the respective sensor units 20, 20a, 29 b, 20 c, 20′, 20 a′, 29 b′, 20 c′ are interposed between therolling elements such as the balls 8, 8, in case where the insidediameter of the mounting hole 15 a for insertion of the sensor units 20,20 a′, 29 b, 20 c, 20′, 20 a′, 29 b′, 20 c′ increases, the rollingbearing unit increases in size in order to secure the strength of theouter ring 1, which increases the manufacturing cost of the rollingbearing unit and raises structural problems such as the reduction inrigidity of the rolling bearing unit. To cope with these problems,preferably, parts large in size such as the vibration sensors 32, 32a-32 f and waveform shaping circuit 29 shown in FIGS. 4A to 6C, withrespect to the axial direction of the holders 24, 24 a-24 c, may bedisposed in series with the magnet detect element 27 (in case where thepermanent magnet 28 is disposed, in series with the permanent magnet 28as well) and nearer to the base end side (in FIGS. 2, 3, 7, 8, 10-13)than these components 27, 28, thereby reducing the diameter of the holes24, 24 a-24 c which are to be inserted into the mounting hole 15 a.

While the preferred embodiments of a wheel rotation detecting deviceaccording to the invention are as described hereinbefore, by using awheel rotation detecting device according to the invention, theabnormality detection of a wheel supporting rolling bearing unit can beexecuted with high reliability. Description will be given below of thereasons for this and five specific examples of a circuit used to detectthe abnormality. By the way, to detect the abnormality of the rollingbearing unit, conventionally, there is generally used a method in whicha temperature sensor is assembled to the rolling bearing unit and, inaccordance with a temperature signal detected by the temperature sensor,the presence or absence of the abnormality is judged. However, in thisconventional method for detecting the presence or absence of theabnormality by detecting the temperature, the abnormality caused by anincrease in the temperature due to poor lubrication such as deterioratedgrease can be detected, but it is difficult to detect an abnormalitycaused by a micro flaking produced in the rolling contact surface of therolling bearing.

Also, in the case of a rolling bearing unit which is incorporated intothe rotation support part of a moving body such as a car, since therolling bearing unit is not rotated at a constant speed all the time,generation of heat due to the friction loss of the rolling bearing unitis not constant. In other words, even in the case of a normal rollingbearing unit, the temperature thereof always varies according tovariations in the rotation speed thereof, which makes it difficult tojudge the presence or absence of the abnormality of the rolling bearingunit only by detecting the temperature variations. That is, thethreshold value of the temperature for judgment of the presence orabsence of the abnormality of the rolling bearing unit must be specifiedwith the high-speed rotation time, in which the temperature rises, as areference; and, therefore, in many cases, it is impossible to detect theabnormality that occurs in the low-speed operating time. Under thesecircumstances, there is a demand to establish a technique which canjudge the abnormality detection of the rolling bearing unit with otherelements than the temperature taken into account to thereby be able toenhance the detection accuracy of the abnormality. A wheel rotationdetecting device according to the invention provides a structure whichis ideal for detection of the abnormality with enhanced accuracy.

Thus, in order to meet the above demand, according to the invention,there is provided a processor for processing signals obtained in a wheelrotation detecting device according to the invention. Now, descriptionwill be given below of five specific examples of the present processor.

Firstly, FIG. 14 is a block diagram of a first example of the processor.The first example judges whether an abnormality is present or not in therolling bearing unit from the rotation speed of a rotary ring of arolling bearing unit that can be obtained from the detect signal of therotation detecting sensor 25 and also from the temperature of therolling bearing unit that can be obtained from the detect signal of thetemperature sensor 26. In the first example, in accordance with a speedsignal representing a value on the rotation speed of the rotary ringthat is obtained by a rotation speed detecting circuit 36 for processingthe detect signal of the rotation detecting sensor 25, a threshold valuesetting circuit 37 determines a threshold value for detection of theabnormality. And, a comparator 38 compares this threshold value with thetemperature signal transmitted from the temperature sensor 26, and abearing abnormality determination circuit 39 checks a signalrepresenting the above comparison result to thereby judge the presenceor absence of the abnormality in the rolling bearing unit. Then, if theabnormality is present, a signal is transmitted to an alarm 40 such as abuzzer or a warning light to thereby operate the alarm 40, so that thealarm 40 gives the driver an alarm that notifies the occurrence of theabnormality. In the thus-structured processor according to the presentexample, in accordance with variations in the rotation speed of therolling bearing unit that can be obtained from the detect signals of therotation detecting sensor 25, the threshold value of the temperature fordetection of the abnormality is varied sequentially (that is, thethreshold value is increased as the rotation speed is increased),thereby being able to detect the abnormality of the rolling bearing unitwhich occurs not only in the high-speed rotation time but also in thelow-speed rotation time.

Next, FIG. 15 is a block diagram of a second example of the presentprocessor. The second example also judges whether an abnormality ispresent or not in the rolling bearing unit from the rotation speed of arotary ring of a rolling bearing unit that can be obtained from thedetect signal of the rotation detecting sensor 25 and from the vibrationof a rolling bearing unit that can be obtained from the detect signal ofthe vibration sensor 32. In the second example, a threshold value fordetection of an abnormality relating to the vibration is set inaccordance with a speed signal which can be obtained from the detectsignal of the rotation detecting sensor 25, a comparator 38 a comparesthis threshold value with a signal from the vibration sensor 32, and abearing abnormality determination circuit 39 a judges the presence orabsence of the abnormality in the rolling bearing unit. In thethus-structured processor according to the present example, inaccordance with variations in the rotation speed of the rolling bearingunit, the threshold value of the vibration for detection of theabnormality is varied sequentially (that is, the threshold value isincreased as the rotation speed is increased), thereby being able todetect the abnormal vibration of the rolling bearing unit which occursin the low-speed rotation time. Therefore, it is possible to detect inan early stage even a slight flaking which is produced in the rollingcontact surface of the rolling bearing unit.

That is, generally, the vibration occurring in the operating time of therolling bearing unit increases as the rotation speed increases. For thisreason, when judging the presence or absence of the abnormality of therolling bearing unit only from the detect signal of the vibrationsensor, the threshold value for detection of the abnormality need to beset in correspondence to the value of vibrations occurring in the timewhen the rotation speed is the largest that can be expected. Due tothis, it is difficult to detect the abnormality of the rolling bearingunit in the low-speed rotation time. On the other hand, with use of aprocessor according to the present example, since the threshold valuefor detection of the abnormality can be varied sequentially according tothe then rotation speed, the abnormality such as the flaking can bedetected with high reliability in accordance with the level of thevibration.

Next, FIG. 16 is a block diagram of a third example of the processor.The third example also judges whether an abnormality is present or notin the rolling bearing unit from the rotation speed of a rotary ring ofa rolling bearing unit that can be obtained from the detect signal ofthe rotation detecting sensor 25 and from the vibration of a rollingbearing unit that can be obtained from the detect signal of thevibration sensor 32. Especially, in the third example, a signal, whichis issued from the vibration sensor 32 and represents the vibration ofthe rolling bearing unit, is passed through a variable filter 41. Thisvariable filter 41 varies a removing frequency or a damping frequency inaccordance with a signal which can be obtained from the detect signal ofthe rotation detecting sensor 25 for representation of the rotationspeed of the rolling bearing unit. A vibration value, which is obtainedafter the rotation speed component of the rolling bearing unit isremoved or dampened, is compared with a threshold value for detection ofthe abnormality obtained similarly to the previously described secondexample by a comparator 38 a, and a bearing abnormality determinationcircuit 39 a judges whether an abnormality is present or not in therolling bearing unit.

In the case of the vibration which occurs while a rolling bearing unitis rotating, generally, the value of the vibration of the rotation speedcomponent synchronized with the rotation speed is the largest; however,in case where damage such as a flaking occurs at raceways or rollingelement surfaces of the rolling bearing unit, the value of the vibrationof the frequency component not synchronized with the rotation speedincreases. In view of this, in the present example, by passing thesignal representing the vibration of the rolling bearing unit throughthe variable filter 41 which varies the removing or damping frequencybased on the signal of the rotation detecting sensor 25, the vibrationvalue of the frequency corresponding to the rotation speed component isremoved or dampened. Therefore, the vibration represented by the signalafter passage through the variable filter 41, even in the normal statethereof, contains no frequency component or only a slight frequencycomponent if any; and thus, the component of the vibration occurring dueto the presence of an abnormality can be detected more clearlyaccordingly. This makes it possible to enhance the accuracy of detectionof the presence or absence of the abnormality in the rolling bearingunit. In other words, in an early stage where a flaking starts to occurin the rolling contact portion of the rolling bearing unit, theabnormality of the rolling bearing unit can be detected, which canprevent serious damage such as seizure from occurring in the rollingbearing unit.

Next, FIG. 17 is a block diagram of a fourth example of the processor.The fourth example also judges whether an abnormality is present or notin the rolling bearing unit from the rotation speed of a rotary ring ofa rolling bearing unit that can be obtained from the detect signal ofthe rotation detecting sensor 25 and from the vibration of a rollingbearing unit that can be obtained from the detect signal of thevibration sensor 32. Especially, in the fourth example, a periodanalysis circuit 42 is used to analyze the period of a vibrationwaveform detected by the vibration sensor 32, thereby being able tojudge whether any abnormality is present or not in the rolling bearingunit. More specifically, to attain this purpose, in the present example,a bearing abnormality determination circuit 39 b, in accordance with arotation speed signal which can be obtained from the detect signal ofthe rotation detecting sensor 25 to represent the rotation speed of therolling bearing unit, calculates the periods T₁, T₂, T₃ of various kindsof vibrations generated from the rolling bearing unit and judges whetherany abnormality is present or not in the rolling bearing unit. By theway, referring more specifically to the respective periods T₁, T₂, T₃,in case where the rolling bearing unit is used in such a manner that itsinner ring rotates, T₁ expresses the period of the vibrations generatedwhen a flaking occurs in an outer ring raceway formed in the innerperipheral surface of an outer ring serving as a stationary ring, T₂expresses the period of the vibrations generated when a flaking occursin an inner ring raceway formed in the outer peripheral surface of aninner ring serving as a rotary ring, and T₃ expresses the period of thevibrations generated when a flaking occurs in the rolling surface of arolling element, respectively. In case where the period of the signalfrom the vibration sensor 32 is analyzed using the rotation speedsignal, not only it can be checked whether damage due to the flaking hasoccurred or not in the rolling bearing unit, but also it is possible tospecify the portion (inner ring raceway, outer ring raceway or rollingelements) of the rolling bearing unit where the flaking has occurred.

For example, when the rolling bearing unit is used in such a manner thatits inner ring rotates, in case where a flaking is caused in the outerring raceway formed in the inner peripheral surface of the outer ringserving as the stationary ring, there are generated vibrations havingthe period expressed by the following expression.That is, T ₁=1/f ₁=1/(z·fc)where f₁: the frequency of the vibration, z: the number of rollingelements, and fc: the frequency of the rotation of a retainer.

On the other hand, in case where a flaking is caused in the inner ringraceway formed in the outer peripheral surface of the inner ring servingas the rotary ring, there are generated vibrations having the periodexpressed by the following expression.That is, T ₂=1/f ₂=1/{z·(fr−fc)}where f₂: the frequency of the vibration, z: the number of rollingelements, fr: the frequency of the inner ring, and fc: the frequency ofthe rotation of a retainer.

Further, in case where a flaking is caused in the rolling surface of therolling element, there are generated vibrations having the periodexpressed by the following expression.That is, T ₃=1/f ₃=1/(2·fb)where f₃: the frequency of the vibration and fb: the frequency of therotation of the rolling element about its own axis.

In these cases, the frequencies fc, fr, fb can be calculated, providedthat the specifications of the rolling bearing unit and the rotationnumber thereof are known. Therefore, by analyzing the period of thevibration waveform, it is possible to specify the portion (outer ringraceway, inner ring raceway or rolling element surfaces) of the rollingbearing unit where the flaking has occurred.

Next, FIG. 18 is a block diagram of a fifth example of the processor. Inthe fifth example as well, a bearing abnormality determination circuit39 c judges whether an abnormality is present or not in the rollingbearing unit from the rotation speed of a rotary ring of a rollingbearing unit that can be obtained from the detect signal of the rotationdetecting sensor 25 and from the vibration of a rolling bearing unitthat can be obtained from the detect signal of the vibration sensor 32.Especially, in the fifth example, the waveform itself of the vibrationdetected by the vibration sensor 32 is envelope processed by an envelopeprocessing circuit 43 and, using the thus processed waveform, afrequency analysis circuit 44 analyzes the frequency of the vibration tothereby enhance the accuracy of the frequency analysis.

By the way, in case where a vibration component having other frequenciesthan the frequencies fc, fr, fb respectively corresponding to therespective periods T₁, T₂, T₃ described in the fourth example increases,it is considered that an abnormality has occurred in the other portionof the rolling bearing unit than the rolling contact surface thereof.Therefore, in case where the period of the detect signal of thevibration sensor 32 or the frequency thereof is analyzed by a periodanalysis circuit 42 or a frequency analysis circuit 44, it is possibleto detect the abnormalities that have occurred in the rotation supportpart of the car and its peripheral portions that include the rollingbearing unit and its peripheral portions. In this case, for example, incase where the primary component of the rotation speed has increasedoutstandingly, it is possible to predict a possibility that localizedwear has occurred in a single portion of the wheel or tire due to thetravelling of the car.

At any rate, in case where the setting of the threshold value fordetection of the abnormality in the rolling bearing unit, or the settingof the period or frequency of the vibration to be analyzed is variedsequentially according to variations in the rotation speed using thefive examples of a process circuit respectively shown in FIGS. 14 to 18,it is possible to set the optimum threshold value or the optimum periodor frequency of the vibration corresponding to the state of the rollingbearing unit varying minute by minute, thereby being able to greatlyenhance the accuracy of judgement of the presence or absence of theabnormality in the rolling bearing unit.

By the way, in a structure where not only the rotation detecting sensorbut also the vibration sensor and temperature sensor are combinedtogether, the abnormality of the rolling bearing unit can be detectedfrom both of the temperature and vibration signals. Therefore, theabnormality such as poor lubrication due to the deteriorated lubricant(grease, oil) or the flaking of the rolling contact surface due to thebiting of foreign substances can be detected widely. According to theabove-mentioned rolling bearing unit abnormality detect apparatus, sincethe wheel rotation detecting device according to the invention, whichprovides a signal detect part, incorporates therein not only therotation detecting sensor for detecting the rotation speed but also, asa sensor for detecting the abnormality of the rolling bearing unit, atleast one of the vibration sensor and temperature sensor, theabnormality of the rolling bearing unit can be detected in an earlystage thereof, which makes it possible to effectively prevent theoccurrence of serious damage such as seizure in the present rollingbearing unit.

Since a wheel rotation detecting device according to the invention isstructured and operates in the above-mentioned manner, it is possible torealize a structure which, while controlling an increase in themanufacturing cost and weight thereof, can detect not only the rotationspeed and rotation number of the wheel but also the temperature andvibration of the wheel supporting rolling bearing. And, the wheelrotation detecting device of the invention is able to contribute towardrealizing not only the ABS and TCS but also a system which can predictthe abnormality of the wheel supporting rolling bearing, variations inthe road condition and in the air pressure of the tire, and accelerationor deceleration conditions to thereby control the running state of thecar in the optimum manner. Also, since the rotation detecting sensor andother sensors are formed as an integral body and are thereby structuredcompact, the installation space for the sensors can be reduced and eachof these sensors can be replaced with an existing rotation detectingsensor, it is not necessary to re-design the wheel supporting rollingbearing unit portion of the car and the present wheel rotation detectingdevice can be realized at a low cost.

While only certain embodiments of the invention have been specificallydescribed herein, it will apparent that numerous modifications may bemade thereto without departing from the spirit and scope of theinvention.

1. A wheel rotation detecting device, comprising: a rolling bearing unitincluding: a stationary ring supported on a suspension and beingunrotatable in use; a rotary ring supporting a wheel thereon and beingrotatable with said wheel; and a plurality of rolling elementsrespectively rollably interposed between a stationary side racewayformed in a peripheral surface of said stationary ring and a rotary sideraceway formed in a peripheral surface of said rotary ring; an encodersupported on said rotary ring or on a part mounted on said rotary ringand being rotatable with said rotary ring; a first sensor supported onsaid stationary ring or a part mounted on said stationary ring in such amanner as to be opposed to said encoder, for detecting the rotation ofsaid rotary ring; and at least one second sensor disposed within aholder holding said first sensor, for detecting the condition of saidrolling bearing unit; wherein said holder is retained within a case ofnon-magnetic metal holding said first and second sensors and is made ofsynthetic resin, wherein said sensor outputs a signal used to detectwhen an abnormality is present in said rolling bearing unit or a portionadjoining said rolling bearing unit, and wherein said wheel rotationdetecting device further comprises: a threshold value setting circuitthat sets a threshold value in accordance with the rotation speed ofsaid rotary ring detected by said rotation detecting sensor so as toincrease said threshold value as said detected rotation speed increases;a comparator for comparing said threshold value with the detect signalof said second sensor; and an abnormality judge circuit for judging thepresence or absence of said abnormality in accordance with an output ofsaid comparator.
 2. The wheel rotation detecting device as set forth inclaim 1, wherein said second sensor includes a temperature sensor fordetecting the temperature of said rolling bearing unit.
 3. The wheelrotation detecting device as set forth in claim 2, wherein saidtemperature sensor is disposed on a leading end of said holder in such amanner as to be situated near to an opposed to a peripheral surface ofsaid rotary ring.
 4. The wheel rotation detecting device as set forth inclaim 1, wherein said second sensor includes a vibration sensor fordetecting the vibration of said rolling bearing unit.
 5. The wheelrotation detecting device as set forth in claim 4, wherein saidvibration sensor is one that detects vibrations at least in twodirections.
 6. The wheel rotation detecting device as set forth in claim4, further comprising: a period analysis circuit for analyzing theperiod of the vibration detected by said vibration sensor, andoutputting a signal representing said period; and an abnormalitydetermination circuit for judging the presence or absence of saidabnormality in accordance with said signal representing said period anda signal representing the rotation speed of said rotary ring detected bysaid first sensor.
 7. The wheel rotation detecting device as set forthin claim 4, further comprising: an envelope processing circuit forprocessing a vibration signal output from said second sensor; afrequency analysis circuit, for receiving the processed vibrationsignal, for analyzing said processed vibration signal, and foroutputting a signal representing a period of the processed vibrationsignal; and an abnormality determination circuit for judging thepresence or absence of said abnormality in accordance with said signalrepresenting said period and a signal representing the rotation speed ofsaid rotary ring detected by said first sensor.
 8. The wheel rotationdetecting device as set forth in claim 1, wherein said second sensorincludes a temperature sensor for detecting the temperature of saidrolling bearing unit and a vibration sensor for detecting the vibrationof said rolling bearing unit.
 9. The wheel rotation detecting device asset forth in claim 1, wherein said second sensor includes a vibrationsensor and said vibration sensor is disposed in series with said firstsensor in an axial direction of said holder, and nearer to a base endside of said holder than said first sensor in the axial direction ofsaid holder.
 10. The wheel rotation detecting device as set forth inclaim 1, wherein said encoder is magnetized along a circumferentialdirection thereof and said encoder includes S and N poles disposed on aperipheral surface thereof such that said S and N poles are alternatelysituated at regular intervals along the circumferential directionthereof.
 11. The wheel rotation detecting device as set forth in claim10, wherein said first sensor includes a magnetic detection element anda waveform shaping circuit and does not include a permanent magnet. 12.The wheel rotation detecting device as set forth in claim 1, whereinsaid encoder is magnetized along a circumferential direction thereof andsaid encoder includes S and N poles and non-magnetized areas disposed ona peripheral surface thereof so as to repeat one another at regularintervals along the circumferential direction thereof.
 13. The wheelrotation detecting device as set forth in claim 1, wherein said secondsensor includes an acceleration sensor.
 14. The wheel rotation detectingdevice as set forth in claim 1, wherein said second sensor includes anvibration sensor, and wherein said vibration sensor is disposed inseries with said first sensor in an axial direction of said holder andnearer to a base end side of said holder than said first sensor in theaxial direction of said holder.
 15. The wheel rotation detecting deviceas set forth in claim 1, wherein said second sensor includes anacceleration sensor, and wherein said acceleration sensor is disposed inseries with said first sensor in an axial direction of said holder andnearer to a base end side of said holder than said first sensor in theaxial direction of said holder.
 16. The wheel rotation detecting deviceas set forth in claim 1, wherein said holder holding said first andsecond sensors is made of synthetic resin.
 17. A wheel rotationdetecting device, comprising: a rolling bearing unit including: astationary ring supported on a suspension and being unrotatable in use;a rotary ring supporting a wheel thereon and being rotatable with saidwheel; and a plurality of rolling elements respectively rollablyinterposed between a stationary side raceway formed in a peripheralsurface of said stationary ring and a rotary side raceway formed in aperipheral surface of said rotary ring; an encoder supported on saidrotary ring or on a part mounted on said rotary ring and being rotatablewith said rotary ring; a first sensor supported on said stationary ringor a part mounted on said stationary ring in such a manner as to beopposed to said encoder, for detecting the rotation of said rotary ring;and at least one second sensor disposed within a holder holding saidfirst sensor, for detecting the condition of said rolling bearing unit,wherein said second sensor includes a vibration sensor for detecting thevibration of said rolling bearing unit, further wherein said vibrationsensor is one that detects vibrations at least in two directions,wherein said second sensor outputs a signal used to detect when anabnormality is present in said rolling bearing unit or a portionadjoining said rolling bearing unit, and wherein said wheel rotationdetecting device further comprises: a threshold value setting circuitthat sets a threshold value in accordance with the rotation speed ofsaid rotary ring detected by said rotation detecting sensor so as toincrease said threshold value as said detected rotation speed increases;a comparator for comparing said threshold value with the detect signalof said second sensor; and an abnormality judge circuit for judging thepresence or absence of said abnormality in accordance with an output ofsaid comparator.
 18. The wheel rotation detecting device as set forth inclaim 17, wherein the vibration sensor comprises two components, eachcomponent detecting vibrations in one of the two directions.
 19. Thewheel rotation detecting device as set forth in claim 17, wherein thevibration sensor is one that detects vibrations in three directions. 20.A wheel rotation detecting device, comprising: a rolling bearing unitincluding: a stationary ring supported on a suspension and beingunrotatable in use; a rotary ring supporting a wheel thereon and beingrotatable with said wheel; and a plurality of rolling elementsrespectively rollably interposed between a stationary side racewayformed in a peripheral surface of said stationary ring and a rotary sideraceway formed in a peripheral surface of said rotary ring; an encodersupported on said rotary ring or on a part mounted on said rotary ringand being rotatable with said rotary ring; a first sensor supported onsaid stationary ring or a part mounted on said stationary ring in such amanner as to be opposed to said encoder, for detecting the rotation ofsaid rotary ring; and at least one second sensor disposed within aholder holding said first sensor, for detecting the condition of saidrolling bearing unit, wherein said second sensor includes anacceleration sensor for detecting acceleration of said rolling bearingunit, further wherein said acceleration sensor is one that detectsaccelerations at least in two directions, wherein said second sensoroutputs a signal used to detect when an abnormality is present in saidrolling bearing unit or a portion adjoining said rolling bearing unit,and wherein said wheel rotation detecting device further comprises: athreshold value setting circuit that sets a threshold value inaccordance with the rotation speed of said rotary ring detected by saidrotation detecting sensor so as to increase said threshold value as saiddetected rotation speed increases; a comparator for comparing saidthreshold value with the detect signal of said second sensor; and anabnormality judge circuit for judging the presence or absence of saidabnormality in accordance with an output of said comparator.
 21. Thewheel rotation detecting device as set forth in claim 20, wherein saidacceleration sensor is one that detects accelerations at least in threedirections.
 22. A wheel rotation detecting device, comprising: a rollingbearing unit including: a stationary ring supported on a suspension andbeing unrotatable in use; a rotary ring supporting a wheel thereon andbeing rotatable with said wheel; and a plurality of rolling elementsrespectively rollably interposed between a stationary side racewayformed in a peripheral surface of said stationary ring and a rotary sideraceway formed in a peripheral surface of said rotary ring; an encodersupported on said rotary ring or on a part mounted on said rotary ringand being rotatable with said rotary ring; a first sensor supported onsaid stationary ring or a part mounted on said stationary ring in such amanner as to be opposed to said encoder, for detecting the rotation ofsaid rotary ring; and at least one second sensor disposed within aholder holding said first sensor, for detecting the condition of saidrolling bearing unit, wherein said second sensor includes a vibrationsensor for detecting the vibration of said rolling bearing unit; aperiod analysis circuit for analyzing the period of the vibrationdetected by said vibration sensor, and outputting a signal representingsaid period; and an abnormality determination circuit for judging thepresence or absence of said abnormality in accordance with said signalrepresenting said period and a signal representing the rotation speed ofsaid rotary ring detected by said first sensor.
 23. The wheel rotationdetecting device as set forth in claim 22, wherein the abnormality isthat flaking has occurred in a portion of the rolling bearing unit, andsaid abnormality detecting circuit detects where the flaking hasoccurred based on the signal representing the period.
 24. A wheelrotation detecting device, comprising: a rolling bearing unit including:a stationary ring supported on a suspension and being unrotatable inuse; a rotary ring supporting a wheel thereon and being rotatable withsaid wheel; and a plurality of rolling elements respectively rollablyinterposed between a stationary side raceway formed in a peripheralsurface of said stationary ring and a rotary side raceway formed in aperipheral surface of said rotary ring; an encoder supported on saidrotary ring or on a part mounted on said rotary ring and being rotatablewith said rotary ring; a first sensor supported on said stationary ringor a part mounted on said stationary ring in such a manner as to beopposed to said encoder, for detecting the rotation of said rotary ring;and at least one second sensor disposed within a holder holding saidfirst sensor, for detecting the condition of said rolling bearing unit,wherein said second sensor includes a vibration sensor for detecting thevibration of said rolling bearing unit; an envelope processing circuitfor processing a vibration signal output from said second sensor; afrequency analysis circuit, for receiving the processed vibrationsignal, for analyzing said processed vibration signal, and foroutputting a signal representing a period of the processed vibrationsignal; and an abnormality determination circuit for judging thepresence or absence of said abnormality in accordance with said signalrepresenting said period and a signal representing the rotation speed ofsaid rotary ring detected by said first sensor.
 25. The wheel rotationdetecting device as set forth in claim 24, wherein abnormalities in therolling bearing unit are detected.
 26. A wheel rotation detectingdevice, comprising: a rolling bearing unit including: a stationary ringsupported on a suspension and being unrotatable in use; a rotary ringsupporting a wheel thereon and being rotatable with said wheel; and aplurality of rolling elements respectively rollably interposed between astationary side raceway formed in a peripheral surface of saidstationary ring and a rotary side raceway formed in a peripheral surfaceof said rotary ring; an encoder supported on said rotary ring or on apart mounted on said rotary ring and being rotatable with said rotaryring; a first sensor supported on said stationary ring or a part mountedon said stationary ring in such a manner as to be opposed to saidencoder, for detecting the rotation of said rotary ring; and at leastone second sensor disposed within a holder holding said first sensor,for detecting the condition of said rolling bearing unit, wherein saidencoder is magnetized along a circumferential direction thereof and saidencoder includes S and N poles and non-magnetized areas disposed on aperipheral surface thereof so as to repeat one another at regularintervals along the circumferential direction thereof; wherein saidsecond sensor outputs a signal used to detect when an abnormality ispresent in said rolling bearing unit or a portion adjoining said rollingbearing unit, and a threshold value setting circuit that sets athreshold value in accordance with the rotation speed of said rotaryring detected by said rotation detecting sensor so as to increase saidthreshold value as said detected rotation speed increases; a comparatorfor comparing said threshold value with the detect signal of said secondsensor; and an abnormality judge circuit for judging the presence orabsence of said abnormality in accordance with an output of saidcomparator.
 27. A wheel rotation detecting device, comprising: a rollingbearing unit including: a stationary ring supported on a suspension andbeing unrotatable in use; a rotary ring supporting a wheel thereon andbeing rotatable with said wheel; and a plurality of rolling elementsrespectively rollably interposed between a stationary side racewayformed in a peripheral surface of said stationary ring and a rotary sideraceway formed in a peripheral surface of said rotary ring; an encodersupported on said rotary ring or on a part mounted on said rotary ringand being rotatable with said rotary ring; a first sensor supported onsaid stationary ring or a part mounted on said stationary ring in such amanner as to be opposed to said encoder, for detecting the rotation ofsaid rotary ring; and at least one second sensor disposed within aholder holding said first sensor, for detecting the condition of saidrolling bearing unit, wherein said second sensor outputs a signal usedto detect when an abnormality is present in said rolling bearing unit ora portion adjoining said rolling bearing unit, and wherein said wheelrotation detecting device further comprises: a threshold value settingcircuit that sets a threshold value in accordance with the rotationspeed of said rotary ring detected by said rotation detecting sensor soas to increase said threshold value as said detected rotation speedincreases; a comparator for comparing said threshold value with thedetect signal of said second sensor; and an abnormality judge circuitfor judging the presence or absence of said abnormality in accordancewith an output of said comparator.
 28. The wheel rotation detectingdevice as set forth in claim 27, wherein said second sensor includes atemperature sensor for detecting the temperature of said rolling bearingunit.
 29. The wheel rotation detecting device as set forth in claim 27,wherein said second sensor includes a vibration sensor for detecting thevibration of said rolling bearing unit.
 30. The wheel rotation detectingdevice as set forth in claim 29, further comprising: a variable filterpassing a signal detected by said vibration sensor, wherein the variablefilter varies a removing frequency or a damping frequency in accordancewith the rotation speed.
 31. The wheel rotation detecting device as setforth in claim 27, wherein said second sensor includes an accelerationsensor for detecting the vibration of said rolling bearing unit.
 32. Thewheel rotation detecting device as set forth in claim 27, wherein saidwheel rotation detecting device further includes a variable filterpassing a signal detected by said acceleration sensor, wherein thevariable filter varies a removing frequency or a damping frequency inaccordance with the rotation speed.